Hydrazine decomposition process using molybdenum catalyst

ABSTRACT

THIS INVENTION RELATES TO A PROCESS FOR THE SPONTANEOUS CATALYTIC DECOMPOSITION OF ROCKET PROPELLANTS CONTAINING HYDRAZINE OR MIXTURES OF HYDRAZINE AND HYDRAZINE NITRATE. THE CATALYST USED IN THIS INVENTION RETAINS ITS ACTIVITY AFTER EXPOSURE TO THE PROPELLANT FLAME ENVIRONMENT THEREBY PERMITTING MULTIPLE STARTS OF A ROCKET ENGINE. THE CATALYST CONSISTS OF MOLYBDENUM METAL COATED ON A HIGH SURFACE AREA SUPPORT BODY SUCH AS ALUMINA, IRON, NICKEL, COPPER, IRIDIUM, OR RUTHENIUM MAY BE INCLUDED AS CO-CATALYST METALS.

United. States Patent 3,608,313 HYDRAZINE DECOMPOSITION PROCESS USING A MOLYBDENUM CATALYST Eugene D. Guth, Palos Verdes Peninsula, and Jack L. Blumenthal, Los Angeles, Calif., assignors to TRW Inc., Redondo Beach, Calif. No Drawing. Filed Dec. 16, 1966, Ser. No. 602,115

Int. Cl. C06d /04 US. Cl. 60-219 6 Claims ABSTRACT OF THE DISCLOSURE Problems with prior-art hydrazine decomposition catalysts have frequently come from the fact that the catalytic materials are decomposed or reacted at the flame temperature of the propellant. Several catalysts containing cobalt, copper, and alkali metals are known to decompose hydrazine at ambient temperatures, however they are deactivated by flame temperature and thus are suitable for only one start. The transition group metal salts and silver salts also suffer the undesirable property of decomposing at hydrazine flame temperatures. These problems with catalysts did not arise until rocket engine art was extended to include more than one start.

Hydrazine spontaneous decomposition catalysts, according to this invention, are produced by coating molybdenum on a high surface area support, such as alumina, thoria, or zirconia. When desired, a certain degree of enhancement or synergism may be achieved by adding co-catalyst metals such as iron, niclcel, copper, iridium, and ruthenium.

Proportions of the catalytic ingredients are effective over a wide range. Molybdenum may be employed in a range froml60 weight percent of the support particle, however, 5-35 weight percent is generally preferred. Cocatalysts, iron, nickel, copper, iridium, and ruthenium, may be employed in amounts up to 50 weight: percent of the support particle, however, they should be present in minor amounts With respect to the molybdenum and should never exceed the weight percent of the molybdenum present.

Preferably, preparation of the molybdenum catalyst is accomplished by soaking the support body in a saturated solution of ammonium molybdate for at least one hour and decanting the excess molybdate solution. These support pellets are then removed and dried in vacuum at approximately 100 C. Upon completion of the drying Ice step, the catalyst is activated by reduction in a slow moving stream of dry hydrogen at approximately 700 C. One or more promoters or co-catalysts such as iron, nickel, copper, iridium, or ruthenium are applied to the molybdenum catalyst in a similar manner. Support bodies which have been coated with the molybdenum catalyst are immersed in a dilute aqueous solution of a soluble salt of the co-catalyst metal. The excess solution is decanted otf and the catalyst impregnated pellets are dried and reduced in a manner similar to the molybdenum.

The decomposition catalyst described above may be employed for hydrazine, alone, or any hydrazine-containing fuel mixture, such as hydrazine-hydrazine nitrate. Details of catalyst position known in the art may be applied here, i.e., no special considerations are necessary as a result of use of the instant catalysts. Generally, all that is required is that the catalysts come in contact with the hydrazine fuel prior to or during ignition of the fuel as the following example shows.

EXAMPLE A catalyst of the type which is the subject of this invention was used to ignite and decompose a hydrazinehydrazine nitrate mixture in three-pound thrust engine hardware. The catalyst was prepared by the method cited above and contained 8% molybdenum on a high surface area support of Harshaw 1404 Alumina. The fuel used was a monopropellant containing hydrazine and 25% nitrate. It was found that when the fuel was injected into the catalyst bed, smooth, rapid ignition occurred when the actalyst bed was initially at ambient temperature or near the hydrazine flame temperature. The test engine was operated in a pulsed mode of milli-second firings each second and gave reproducible ignition and smooth decomposition of the fuel. In addition, the engine was operated at steady state for more than ten seconds and the catalyst continued to provide smooth decomposition of the hydrazine throughout the firing.

Hydrazine decomposition catalysts, according to this invention, are attractive not only because of the relative ease of preparation, but because of the low cost of the materials employed. In addition, catalysts according to this invention, do not decompose upon exposure to the propellant flame environment. This advantageous property permits multiple reignition of rocket engines, a feat of some difficulty and questionable reliability heretofore.

We claim:

1. A method for decomposing and igniting a hydrazine fuel in a thrust producing engine which comprises contacting propellant fuels selected from the class consisting of hydrazine and hydrazine-hydrazine nitrate at ambient temperatures with a catalyst in a thrust producing engine, said catalyst consisting essentially of at least molybdenum, and a metal selected from the group consisting of iron, nickel, copper, iridium, and ruthenium coated on a high surface area support.

2. A method according to claim 1 wherein the high surface area support is selected from the group consisting of alumina, thoria, zirconia.

3. A method according to claim 1 wherein the catalyst comprises 1-60 weight percent molybdenum and the balance inert ingredients.

4. A method according to claim 1 wherein the catalyst comprises 5-35 weight percent molybdenum and the balance inert ingredients.

5. A method according to claim 1 wherein the catalyst comprises 1-60 weight percent molybdenum, a minor amount of a metal selected from the group consisting of iron, nickel, copper, iridium, and ruthenium, and the balance inert ingredients.

6. A method according to claim 1 wherein the catalyst comprises 5-35 Weight percent molybdenum, a minor amount of a metal selected from the group consisting of balance inert ingredients. 7

References Cited UNITED STATES PATENTS 2/1960 Mantell et a1. 602l8X 2/1960 Plescia et a1. 252474 3/1960 Plescia et al 60218X 2/1962 Griffin et a1 60-218 2/1963 Rose, 60218X 8/1963 Hamrick et al 60220 BENJAMIN R. PADGETT, Primary Examiner US. Cl. X.R. 

